Directed self-assembly is a promising strategy for high-volume cost-effective manufacturing at the nanoscale. Over the past decades, manufacturing techniques have been developed with such remarkable efficiency that it is now possible to engineer complex systems of heterogeneous materials at the scale of a few tens of nanometers to support the every growing market for semiconductors, which exceeded $300 billion in 2010. Further evolution of these techniques, however, is faced with difficult challenges not only in feasibility of implementation at scales of 10 nm and below, but also in prohibitively high capital equipment costs. Materials that self-assemble, on the other hand, spontaneously form nanostructures down to length scales at the molecular scale. The micrometer areas or volumes over which the materials self-assemble with adequate perfection in structure is incommensurate with the macroscopic dimensions of working devices and systems of devices of industrial relevance. Directed Self-Assembly (DSA) refers to the integration of self-assembling materials with traditional manufacturing processes. The key concept of DSA is to take advantage of the self-assembling properties of materials to reach nanoscale dimensions and at the same time meet the constraints of manufacturing. Put another way, DSA enables current manufacturing process capabilities to be enhanced and augmented, providing pathways for true nanomanufacturing at drastically reduced cost.
DSA of block copolymer films on lithographically defined chemically nanopatterned surfaces is an emerging technology that is well-positioned to revolutionize sub 10 nm lithography and the manufacture of integrated circuits and magnetic storage media. See, for example, Nealey, et al., US Patent Application Publication Nos. 2013/0189504 and 2014/0065379 (both of which are incorporated by reference). Block copolymer materials self-assemble to form densely packed features with highly uniform dimensions and shapes in ordered arrays at the scale of 3 to 50 nm. Chemical pre-patterns are defined using traditional lithographic materials and processes such as 193 immersion or electron beam lithography at the scale of 20 to 40 nm. By directing the assembly of block copolymer films on the chemical pre-patterns, the overall resolution of the lithographic process may be increased by three to four-fold or more. This technology can be applied to semiconductors, materials and equipment, and hard drive manufacture. The interest and exponential growth in research activity and expenditure is driven in the semiconductor industry by the prospect of manufacturing future generations of computer chips according to Moore's law without having to invest billions of dollars in new fabrication facilities (i.e., based on extreme ultra violet lithography) that may or may not be able to meet the resolution requirements already being demonstrated by DSA. For example, IBM developed a chip with 7 nm transistors with a silicon-germanium alloy (SiGe). The design was produced using extreme ultraviolet lithography (EUV, =13.5 nm). The chip was faster with higher-capacity and lower power consumption. This chip was lab-scale and highly expensive. For hard drives, block copolymer lithography is the only known technology that is feasible to fabricate nanoimprint masters to manufacture bit patterned media at the required storage densities (at least greater than 2 Terabit/inch2). Currently DSA of poly(styrene-block-methymethacrylate) (PS-b-PMMA) films on lithographically defined chemically nanopatterned surfaces is the primary focus of activity, and the main research objectives revolve around demonstrations that DSA can meet manufacturing requirements related to degrees of perfection, processing latitude, and integration of the technology with existing infrastructure, and device design for use with DSA patterns.
Critical research issues must be addressed in order to push the DSA technology over the tipping point to widespread implementation in nanomanufacturing. A key roadblock is the establishment of proven pathways to realize sub 10 nm resolution, and scaling to 5 nm; the resolution limit of PS-b-PMMA is ˜12 nm. Neither the semiconductor industry nor the hard drive industry will implement DSA for a single generation of products. Whereas substantial effort is being expended by many groups to identify block copolymer systems capable of self-assembling into the sub 10 nm regime, technology gaps exist in fundamental and technological understanding as to how those materials may be processed and directed to assemble and continue to meet the constraints of manufacturing. Moreover, little or no work is aimed at developing specialized tools and processes that will be applicable at the ultimate end-of-the-roadmap length scale.
Directed self-assembly of block copolymers uses physical and/or chemical pre-patterns to control the orientation and alignment of block copolymers (e.g., FIG. 1 and FIG. 2). Strongly segregating block copolymers (high Flory-Huggins parameter (χ), related to the energy of mixing) can produce higher resolution patterns. The Flory-Huggins parameter also indicates the incompatibility of copolymers. Because such block copolymers typically show large differences in surface energy between the blocks, one block (with lower surface energy) tends to segregate to the free surface of films and precludes the assembly of the desired through-film perpendicularly oriented structures during thermal annealing. The low-surface-energy domain of the block copolymer tends to wet the top surface and disrupt the perpendicular orientation of the block copolymers. A topcoat on the block copolymer can inhibit the disruption of the polymer orientation. In this case, thermodynamically favorable boundary conditions at the top surface of the film can be engineered for directed self-assembly. However, the topcoat material and coating methods are limited. Solution spin-coating usually dissolves block copolymers.
There exists a need to develop alternative sub-10 nm patterning methods. These methods can be used to develop faster devices with higher-capacity and lower power consumption. The methods should be compatible with current manufacturing methods and avoid expensive investment in new fabrication facilities.